HR: 09:45h
AN: G51D-08    [Abstracts]
TI: Error Evaluations of GPS Estimates in Active Weather Conditions Based On High-Resolution Numerical Weather Model
AU: * Iwabuchi, T
EM: iwabuchi@ucar.edu
AF: UCAR COSMIC Program, 3300 Mitchell Lane, Boulder, CO 80301, United States
AU: Rocken, C
EM: rocken@ucar.edu
AF: UCAR COSMIC Program, 3300 Mitchell Lane, Boulder, CO 80301, United States
AB: Mitigations of effects of microwave propagation delay due to water vapor have been discussed in GPS communities for more than 10 years. It is furthermore important in the current era of real-time monitoring of kinematic coordinates and precipitable water vapor (PWV). The significant errors in coordinate estimates are usually observed in summer and in active weather conditions, and they should be mitigated to prevent misleading in geodynamical discussions. Quantitative estimation of errors in GPS estimates in such cases and understandings of mechanism of the errors are important for further improvement of GPS tropospheric models. In the present circumstances, the output from numerical weather model are only 3-dimensional data which can be used to validate atmospheric models used in GPS processing if the model can reproduce realistic variations of water vapor. We thus compute errors of GPS estimates from high-resolution NWP output and discuss limitation of the current tropospheric models used in GPS processing. We focused on several active weather conditions with severe precipitation, and performed high-resolution simulations with Weather Research and Forecasting (WRF) model. To reproduce realistic variations of water vapor, the horizontal scale was set to 4 km to avoid a cumulus parameterization. The forecast output is every 30 seconds which is equal to sampling rate in general GPS observation. We computed slant wet delay by ray-tracing of wet refractivity with actual GPS orbit information at real (SUOMINET) and imaginary GPS stations in the U.S. Wet mapping function, tropospheric wet delay gradients, and zenith wet delays were computed based on the slant wet delay, where reasonable constrains which is used in GPS processing were applied in the estimates. The estimates based on whole coverage of sky were also computed to evaluate errors came from inhomogeneous coverage of GPS satellite in particular axis (usually north-south axis). The residuals of slant wet delays from model fits are used to estimate coordinate errors. We also estimated representive errors for time and space in GPS retrieved precipitable water vapor (PWV) due to limitation of GPS tropospheric models and limited coverage of GPS satellites in the sky. Such information would be useful to decide both observation and representive errors used in data assimilation.
UR: http://www.cosmic.ucar.edu/~iwabuchi
DE: 1220 Atmosphere monitoring with geodetic techniques (6952)
DE: 1241 Satellite geodesy: technical issues (6994, 7969)
DE: 1243 Space geodetic surveys
SC: Geodesy [G]
MN: 2007 Fall Meeting